The present invention relates to a method of forming a bore for attachment of a suture, in a proximal end portion of an eyeless operating needle.
An eyeless operating needle has a proximal end portion formed therein with a bore of a predetermined depth extending along the axis of the needle. An end of a suture is inserted into the bore and, subsequently, the proximal end portion of the needle is staked, to thereby attach the suture to the needle.
There are various manners of forming the bore, such as, for example, a drilling machining, electric discharge machining, laser beam machining, electron beam machining and the like. When the needle is particularly small in diameter, machinings are employed which utilize a beam energy such as laser, electron or the like, in which the material of the needle is sublimated by the beam energy to form a bore therein. Various improvements have been proposed with respect to such machinings using the beam energy, as has been disclosed in Japanese Patent Application Laid-Open Nos. 52-111294, 60-170590 and 60-184485, Japanese Utility Model Publication No. 56-37918, Japanese Utility Model Application Laid-Open No. 55-43691 and the like.
However, in case where the needle is small in outer diameter and the wall thickness surrounding the bore formed in the proximal end portion of the needle is thin, for example, when a bore is formed, by the beam energy, in a needle which is used in brain operations or the like, a rate or percentage of occurrence of defective needles has been very high, in which a bore 105 is bent with respect to a center axis of a needle 100 as shown in FIG. 9 of the accompanying drawings, or a part of a wall surrounding a bore 105 is destroyed as shown in FIGS. 10 and 11.
The inventor of the present application has considered and presumed causes of the occurrence of the above-noted defects as follows. That is, the beam is a pulse of short time duration on the order of 0.001 second, but the inside of the wall surrounding the bore is brought to a high temperature on the order of 10,000.degree. C. Moreover, there is almost no heat radiation or diffusion, because the outside of the wall is air which is low in thermal conductivity. Accordingly, the wall must have its thickness sufficient to withstand the given heat energy. For example, however, when the center of the beam is not coincident with the center of the end face of the proximal end portion of the needle, a specific portion of the wall surrounding the bore becomes further thin, and the wall thickness of the specific portion would be brought to a level lower than the limitative thickness. In addition, if the energy distribution of the beam is deviated, the wall thickness of a portion to which the heat energy is concentrated is brought to a level lower than the allowable level. The inventor has presumed, this would result in the occurrence of the above-mentioned defective needles.